The present invention relates to a turbine housing for an exhaust gas turbocharger with an adjustable turbine geometry.
Exhaust gas turbochargers in which the boost pressure can be regulated by adjustable guide vanes are known from German Patent DE 103 12 324 B3, for example. A guide vane apparatus, consisting of a carrier ring for the guide vanes and a cover ring which is opposite the carrier ring, is mounted in the turbine housing of such chargers having a variable turbine geometry (VTG), maintaining a guide vane gap distance. Spacer elements, e.g., in the form of spacer sleeves held by fastening screws, for example, are distributed radially around the circumference of the two rings to maintain a distance from the carrier ring and the cover ring. When using these VTG chargers in gasoline engines in particular, these components are exposed to high exhaust gas temperatures. A durable screw connection of the spacers is especially critical here. If the spacer elements are exposed to the hot exhaust gas flow, they will expand accordingly in the longitudinal direction while the fastening screws are still relatively cold. Conversely, when there is a subsequent jump in load (full load in the direction of low partial load), the spacer element is first cooled by the exhaust gas stream while the fastening screw is still relatively hot. This results in more rapid shrinkage of the spacer element over time in comparison with the fastening screw and thus results in a corresponding loss of prestress power. Due to the loss of prestress power, the fastening screw must now absorb all the transverse forces occurring due to engine operation, which under some circumstances will result in component failure of the fastening screw.
An object of the present invention is to overcome the disadvantages described above in order to ensure safe, reliable, continuous operation of the VTG charger.
A durable screw connection without any loss of prestress power is ensured by an additional form-fitting connection between the fastening screw and the carrier ring or cover ring. For the form-fitting connection, securing recesses are provided in the carrier ring or cover ring in the area of the receiving opening for the head of the fastening screw so that, for example, material of the screw head can be introduced into the securing recesses by caulking by a reshaping operation.
Additional advantageous embodiments and refinements of the turbine housing and/or the guide vane apparatus for a VTG turbocharger are possible through the features characterized in the subclaims.
For example, two securing recesses to receive the screw head material are preferably provided per screw connection, each securing recess being offset 180° on the outside circumference of the recess opening for the screw head. This establishes an optimum form-fitting connection which prevents a loss of prestress power and thus prevents the fastening screw from becoming unscrewed.
The securing recesses may be created mechanically, e.g., by a suitable milling tool, or as an alternative they may be created already in the casting operation, e.g., by the MIM (metal injection molding) method or by the precision casting method to produce the carrier ring or the cover ring.
A good frictionally engaged screw connection of the guide vane apparatus is ensured by using a fastening screw with a countersunk head.
Three receiving openings for the fastening screws are distributed uniformly around the circumference in the carrier ring or cover ring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings for example.